To help me appreciate the amount of honey bee semen that Washington State University entomologists collected for the U.S. Department of Agriculture last year, Steve Sheppard scales up.
Imagine a prize bull, said Sheppard, chair of the university’s entomology department. With the semen from just one ejaculate, they could fill hundreds of thousands of straws the size of a swizzle stick. But each drone — a male honey bee — produces a microliter of semen at most. It takes about 20 hardy drones to produce enough semen to fill one of those straws. Last year, they filled 21 from several hundred drones.
“If you were looking at bulls,” Sheppard said, “you’d need a warehouse.”
Instead, the honey bee semen samples are frozen in liquid nitrogen and stored in Fort Collins, CO, at the National Laboratory for Genetic Resources Preservation. Since 1958, the U.S. Department of Agriculture Research Service, which is part of the USDA, has maintained hundreds of thousands of samples of seeds there in vaults designed to withstand floods, tornadoes and — the government’s words — “the dropping of a 2,500 pound object traveling at 125 miles per hour.” It’s the world’s largest collection of seeds that are kept in case of disasters that could wipe out a crop. In that spirit, the lab also stores the germplasm, or genetic material of germ cells, from plants, animals, and, as of last year, honey bees.
The new National Bee Genebank is aimed in part at helping the beekeeping industry mitigate losses from pathogens and parasites, including the Varroa mite that has ravaged honey bee colonies in the past few decades. Colony Collapse Disorder, in which the majority of worker bees that sustain a hive disappear, has also caused a contraction in genetic variability, according to Harvey Blackburn, an animal geneticist at the lab. By collecting semen samples now, beekeepers can use them in later years to bolster struggling colonies, and maybe breed better bees. By crossing the genes from an older, frozen population with a current one, breeders could produce gentler bees that make more honey and are more resistant to pests and disease.
“It’s a food security issue,” Blackburn said. He pointed to California’s lucrative almond industry. “That is all made possible by honey bees being put in almond groves to pollinate the flowers.”
Sheppard and Brandon Hopkins, who developed the technology that’s enabled scientists to freeze bee semen indefinitely, will head back to California in May to continue the work they started nearly a year ago gathering germplasm for the genebank. Last spring, they collected honey bee samples from three commercial queen bee producers, squeezing a drone’s abdomen until he ejaculates and then cooling the semen from room temperature to refrigerator temperature over two hours. The semen is then slowly frozen by cooling it three more degrees every minute until it reaches -40 degrees Celsius. Next, the straws are plunged directly into liquid nitrogen and kept at -196 degrees Celsius at the genebank until they’re needed.
Hopkins called the collections a safety net for future breeders.
“Thirty years ago we didn’t have Varroa mites in the United States and now it’s one of the biggest problems for commercial breeders,” he said. “Who’s to say what will be the biggest problem 30 years from now.”
Jackie Park-Burris, one of the queen producers who donated her drones to the research last year, is a second-generation beekeeper. Her family has been breeding bees for about 75 years now. When her father was alive, he battled American foulbrood, a destructive honey bee disease that can badly weaken or even kill a colony. It wasn’t until the end of his life that the family started having serious conversations about Varroa mites, said Park-Burris, who owns Jackie Park-Burris Queens. Now that the mites are plaguing beekeepers, Park-Burris wishes she had some stock stashed in the freezer from back in her dad’s day to help combat them. She likens the samples stored in the genebank to unknown DNA discovered at a crime scene that later leads to an arrest.
“They didn’t know when they saved it that they’d be able to pull it out in 18 years and tell you who did it,” she said.
Last year, the USDA’s National Agriculture Statistics Service released the results of its first Honey Bee Colony Loss survey reflecting the experiences of more than 20,000 honey beekeepers in the country. Beekeepers with five or more colonies reported that Varroa mites were the leading stressor on the colonies. The survey also found that there were 2.59 million, or 8%, fewer honey bee colonies in the country in January 2016 than in January 2015. Colony Collapse Disorder was a likely culprit for the loss of 113,930 colonies in the first quarter of 2016. More than 92,000 were lost during that same period in 2015.
Research has shown that genetic diversity is crucial for honey bee colonies. A 2013 study from North Carolina State University, for example, found that a colony is less likely to survive if its queen has had a limited number of mates. Nearly 50% of colonies with queens who had mated at least seven times were still alive at the end of a 10-month work season while only 17% of less genetically diverse colonies survived, according to the university.
Most beekeepers in the United States are managing the same subspecies of honey bee, the Italian Apis mellifera ligustica, but there are about two dozen other subspecies in the wild, according to USDA. Eventually, the agency would like to college and store semen from pollinators including non-Apis bees.
Park-Burris, Sheppard, and Hopkins are on a committee with representatives from USDA, academia, and industry to help the genebank figure out which bee populations it should collect samples from, under what circumstances those samples should be used, and who can use them. The committee has advised that scientists like Sheppard and Hopkins should first seek samples from some of the country’s major producers who have plenty of drones to sacrifice before moving on to more elusive populations, such as a feral group of bees that survived a Varroa mite infestation and lives in the Arnot Forest in New York. That population may have special characteristics that has helped it survive without human influence that could aid producers who are struggling with their own colonies, Hopkins said.
But really, any bee population could have characteristics that will help producers in the future, he added. Just because they don’t seem valuable right now doesn’t mean they won’t be in the face of climate change, disease, or another unknown threat. Greater genetic diversity makes bee populations more adaptable, he said, so the more they can preserve now, the safer the bees will be.